The invention relates to the field of thermomagnetic recording and more specifically to control of the radiation source in thermomagnetic recording.
The invention relates to a device having a first operational state for writing information onto a record carrier, including
a phase-locked loop for generating, in the first operational state, a clock signal from a reference signal,
a control unit for generating, in the first operational state, a pulsed transducer control signal in response to an information signal and the clock signal,
a transducer for generating, in the first operational state, physically detectable patterns in the record carrier in response to the transducer control signal.
A device of this type is known from U.S. Pat. No. 5,126,985. The device is suitable for writing information onto a record carrier of the thermomagnetic type. In the known device, the transducer for generating, in the first operational state, physically detectable patterns in the record carrier includes an optical write head and a magnetic write head. The device is provided with a synchronizing circuit for generating control signals from the information signal for the optical write head and the magnetic write head. The synchronizing circuit includes a phase-locked loop which generates a clock signal from the information signal. Here the pulse-generator is provided by a delay unit. The pulsed transducer control signal generated by the pulse-generator is provided by the clock signal delayed in the delay unit. This transducer control signal is a response to the clock signal and the information signal. The feedback signal-generator for generating a feedback signal in response to the clock signal is provided by a connection between the controllable oscillator and the error signal-generator. The error signal-generator includes apparatus for generating an instantaneous error signal which is a measure of the instantaneous difference in phase between the information signal and the clock signal which has been fed back. The error signal-generator also includes a loop filter generating an error signal from the instantaneous error signal, which is a measure of an average difference in phase between the information signal and the feedback signal. In this case, the control signal-generator is provided by a direct connection between the loop filter and the controllable oscillator. The error signal is used as a control signal.
When optically reading information from a record carrier, a read head provided with a radiation source is usually used. A radiation beam generated by the radiation source is imaged on the record carrier. By detecting radiation reflected by the record carrier, a read signal can be generated which represents the information recorded on the record carrier.
The above citation is hereby incorporated herein in whole by referenced.
The inventors recognize radiation sources used for these purposes exhibit noise which can be called xe2x80x9crelative intensity noisexe2x80x9d. This is a drawback because this noise also leads to disturbances in the read signal.
It is an object of the invention to provide a device of the type described in the opening paragraph, in which the influence of relative intensity noise when reading a record carrier is limited. According to the invention, the device has a second operational state for reading information from a record carrier. The device includes a transducer for generating, in the second operational state, a read signal in response to physically detectable patterns in the record carrier. The transducer for generating the read signal includes a radiation source. The also includes a power supply which supplies. The radiation source with an electric power, the phase-locked loop includes a memory for memorizing, in the first operational state, a memory value which is a measure of the supplied clock signal, while, in the second operational state, the phase-locked loop generates the clock signal in response to the memorized memory value, and, causes a high-frequency modulation in the electric power supplied by the power supply.
In the device according to the invention, the power with which the radiation source is fed is high-frequency modulated, for example, at a frequency of several hundred MHz, for example, 500 MHz. The inventors have found that this reduces the influence of relative intensity noise. In the device according to the invention, no separate oscillator is necessary for high-frequency modulation of the power for the radiation source. The controllable oscillator, which, in the first operational state, supplies the clock signal for the pulse-generator, functions, in the second operational state, as an oscillator for causing the high-frequency modulation.
These and other aspects of the invention are apparent from and will be elucidated in the description the embodiments described hereinafter with reference to the following drawings which illustrate the element of the claimed invention.